In the conventional method of sealing metallic parts in an X-ray Lube made of glasses, a glass bulb is made closer to a metallic joint of an anodic part and a beryllium window part in thermal expansion coefficient and they are simultaneously heated with a powerful fire to directly weld glasses to metals. However, a serious problem has occurred in that a difficult and dangerous operation requiring great skill is required with an increase in size and the productivity cannot be always improved even though a quantity is increased.